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Mystery of déjà vu explained – it’s how we check our memories

Looks familiar…

Daniel Högberg/plainpicture

By Jessica Hamzelou

Feel like you’ve read this before? Most of us have experienced the eerie familiarity of déjà vu, and now the first brain scans of this phenomenon have revealed why – it’s a sign of our brain checking its memory.

Déjà vu was thought to be caused by the brain making false memories, but research by Akira O’Connorat the University of St Andrews, UK, and his team now suggests this is wrong. Exactly how déjà vu works has long been a mystery, partly because its fleeting and unpredictable nature makes it difficult to study. To get around this, O’Connor and his colleagues developed a way to trigger the sensation of déjà vu in the lab.

The team’s technique uses a standard method to trigger false memories. It involves telling a person a list of related words – such as bed, pillow, night, dream – but not the key word linking them together, in this case, sleep. When the person is later quizzed on the words they’ve heard, they tend to believe they have also heard “sleep” – a false memory.

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To create the feeling of déjà vu, O’ Connor’s team first asked people if they had heard any words beginning with the letter “s”. The volunteers replied that they hadn’t. This meant that when they were later asked if they had heard the word sleep, they were able to remember that they couldn’t have, but at the same time, the word felt familiar. “They report having this strange experience of déjà vu,” says O’Connor.

Brain conflict

His team used fMRI to scan the brains of 21 volunteers while they experienced this triggered déjà vu. We might expect that areas of the brain involved in memories, such as the hippocampus, would be active during this phenomenon, but this wasn’t the case. O’Connor’s team found that the frontal areas of the brain that are involved in decision making were active instead.

O’Connor presented these findings at the International Conference on Memory in Budapest, Hungary, last month. He thinks that the frontal regions of the brain are probably checking through our memories, and sending signals if there’s some kind of memory error – a conflict between what we’ve actually experienced and what we think we’ve experienced.

“It suggests there may be some conflict resolution going on in the brain during déjà vu,” says Stefan Köhler at the University of Western Ontario in Canada.

A healthy head

If these findings are confirmed, they suggest that déjà vu is a sign that your brain’s memory checking system is working well, and that you’re less likely to misremember events.

This would fit with what we already know about the effects of age on memory – déjà vu is more common in younger people and trails off in old age, as memory deteriorates. “It may be that the general checking system is in decline, that you’re less likely to spot memory mistakes,” says O’Connor.

Christopher Moulin at Pierre Mendès-France University in Grenoble says the findings do not bode well for people who don’t experience déjà vu at all. “Without being unkind, they don’t reflect on their memory systems,” he says.

But people who don’t experience déjà vu might just have better memory systems in the first place, says O’Connor. If they’re not making memory errors, there’s no trigger for déjà vu, he says.

We still don’t know if déjà vu is beneficial, says Köhler. “It could be that déjà vu experiences make people cautious, because they might not trust their memory as much,” he says. “But we don’t have any evidence for that yet.”